Speciation sulfur

It is apparent that elemental sulfur species that are suspected to cause silver corrosion can be detected at the appropriate levels that contribute to the fuel gauge issue. Of course, the ability to make a rapid total sulfur measurement is extremely useful in many circumstances. For instance, in a process plant upset, speciation of sulfur may be desirable only when a total sulfur specification is exceeded. In those circumstances, it is desirable to be able to simply change operating conditions back and forth between total sulfur and speciated sulfur analysis, and this is achievable using LTMGC. 

To demonstrate the potential for application at even lower level sulfur fuels, the California reference gasoline was diluted by 10 times in a sulfur-free toluene solvent and re-analyzed. Results fiom this test are illustrated in the small insert of Fig. 11. The results show that this technique is capable of detecting and speciating sulfur at levels even lower than the 5 ppm total sulfur level. On the other hand, it is likely that regulations may mandate sulfur concentrations in fuels at even lower levels. The insert also illustrates that the dilution of the sample to 90 % toluene has little effect on the sulfur distribution, and clearly no hydrocarbon interference is observed. Loss of resolution of the 2 and 3-methylthiophene isomers (eluted just prior to 2 min) was observed due to a chromatographic solvent effect, but otherwise this did not significantly impact the results. 

KEYAVORDS Gas chromatography, atomic emission detection, hetero-atom speciation, sulfur, comprehensive two-dimensional gas chromatography, comprehensive two-dimensional gas chromatography/AED, GCxGC/AED, GCxGC, fuels, gasolines, jet fiels... 

Chambers, L. and Duffy, M. L., "Determination of Total and Speciated Sulfur Content in Petrochemical Samples Using a Pulsed Flame Photometric Detector," J. Chromatographic Set, Vol. 41, 2003, pp. 528-534. 

Gas chromatography with sulfur selective detection provides a rapid means to identify and quantify sulfur compounds in various petroleum fe and products. Often these materials contain varying amounts and types of sulfur compounds. Many sulfur compounds are odorous, corrosive to equipment, and inhibit or destroy catalysts employed in downstream processing. The ability to speciate sulfur compounds in various petroleum liquid is useful in controlling sulfor compounds in finished products and is frequently more important than knowledge of the total sulfur content alone. 

As a more complex example, we examine the stability of oxidation states of aqueous sulfur as a function of pH. This exercise will bring out the treatment of thermodynamically unstable species and the change of sulfur speciation with pH. 

Steudel R, Steudel Y, Wong MW (2003) Speciation and Thermodynamics of Sulfur Vapor. 230 117-134... 

Application to solid polymer/additive formulations is restricted, for obvious reasons. SS-ETV-ICP-MS (cup-in-tube) has been used for the simultaneous determination of four elements (Co, Mn, P and Ti) with very different furnace characteristics in mg-size PET samples [413]. The results were compared to ICP-AES (after sample dissolution) and XRF. Table 8.66 shows the very good agreement between the various analytical approaches. The advantage of directly introducing the solid sample in an ETV device is also clearly shown by the fact that the detection limit is even better than that reported for ICP-HRMS. The technique also enables speciation of Sb in PET, and the determination of various sulfur species in aramide fibres. ETV offers some advantages over the well-established specific sulfur analysers very low sample consumption the possibility of using an aqueous standard for calibration and the flexibility to carry out the determination of other analytes. The method cannot be considered as very economic. 

Rubisov, D. H. Papangelakis, V. G. Sulfuric acid pressure leaching of laterites—prediction of metal solubilities and speciation analysis at temperature. EPD Congress 1999, Proceedings of Sessions and Symposia held at the TMS Annual Meeting, San Diego, Feb. 28-Mar. 4, 1999, 535-546. 

In this case, the program converges to a relatively oxidized solution in which sulfur speciation is dominated by sulfate species. 

Fig. 12.2. Redox-pH diagram for the Fe-S-H20 system at 100 °C, showing speciation of sulfur (dashed line) and the stability fields of iron minerals (solid lines). Diagram is drawn assuming sulfur and iron species activities, respectively, of 10-3 and 10-4. Broken line at bottom of diagram is the water stability limit at 100 atm total pressure. At pH 4, there are two oxidation states (points A and B) in equilibrium with pyrite under these conditions.

An important simplifying consequence of the use of inverted concentration ratios is that the reaction is independent of O2 concentration, which means that unintended 02 contamination should not distort the data. Because of the complexity of the reaction, the relatively new technique of Matrix Rank Analysis was used to sort out the speciation. This analysis led to the identification of two sulfur-containing intermediates [Fe2(0H)S03]3+ and [Fe(S03]+. Other reactant species known to be present under these conditions include S02, HS03, Fe3+, Fe(OH)2+, and... 

Although the abundance of silver in the Earth s crust is comparatively low (0.07 pgg-1), it is considered an environmental contaminant and is toxic at the nanomolar level. As an environmental pollutant it is derived from mining and smelting wastes and, because of its use in the electrical and photographic industries, there are considerable discharges into the aquatic environment. Consequently, there have been studies on the geochemistry and structure of silver-sulfur compounds [31]. Silver, either bound to large molecules or adsorbed on to particles, is found in the colloidal phase in freshwater. In anoxic sediments Ag(I) can bind to amorphous FeS, but dissolved silver compounds are not uncommon. A more detailed study of silver speciation in wastewater effluent, surface and pore waters concluded that 33-35% was colloidal and ca. 15-20% was in the dissolved phases [32]. 

Being the third most common element (after carbon and hydrogen) in petroleum product, sulfur has been analyzed extensively. Analytical methods range from elemental analyses to functional group (sulfur-type) analyses to structural characterization to molecular speciation (Speight, 2001). Of the methods specified for the... 

Zaback DA, Pratt LM (1992) Isotopic composition and speciation of sulfur in the Miocene Monterey Formation reevaluation of sulfur reactions during early diagenesis in marine environments. Geochim Cosmochim Acta 56 763-774... 

---